As a small company focusing on starting up new ventures we have to think very hard about marketing and how to contact new customers. Since the new spam laws mean that we can´t just bulk email every email address we come accross then we have to get people to the sites and then get them to opt-in to a mailing list. Generally the only way they would do this if there´s some incentive for them.
In the past we´ve done things like "Win a PC" competitions and suych but it still involves getting people to the sites in the first place either through traditional offline marketing or by getting up the SERPs. This means that I spend a lot of time tweaking code and key words to try and boost of search results placing.
We did have the idea of trying to get people to distribute marketing bumf for us. One way of doing this is to create videos of games that people will want to forward to their friends and include links to our sites in them. Just got to think of a few ideas for Flash games and then figure out a way of getting them from the "fun" sites to our more product orientated sites.